In general, speakers phonate in order to convey information (linguistic or paralinguistic; intentionally or unintentionally) to a listener. The stages of transmitting information in this way can be described by the well- known ?speech chain.? We presently know a good deal about the individual steps along the chain, including motor planning, laryngeal innervation, tissue properties, the biomechanics of laryngeal vibrations, aeroacoustics, acoustics and resonance, and voice perception. However, very few studies address the manner in which information is transmitted from one stage to the next, much less from one end of this chain to the other. As a result, two important questions about voice remain unanswered: 1) When voice quality changes in some way, what caused the change? and 2) If a change occurs in the voice production mechanism, what will be the resulting perceived change in quality? In our view, these two questions define the primary goals of the study of voice. By combining computational modeling of voice production and acoustic and perceptual analyses of voice quality, this proposal addresses these critical questions in a series of studies designed 1) to complete final development of a theoretically-motivated measurement protocol for voice quality that enables users to reliably and validly assess the overall, integral quality of a voice; and 2) to develop a causal model linking changes in voice acoustics and quality to underlying physiologic mechanisms. Finally, we will investigate how changes in psychoacoustic or physiologic parameters relate to the extent to which a voice deviates from normal, in a better-to-worse continuum. Such information would facilitate objective and meaningful comparisons across individual patients and clinicians in evaluation and documentation of treatment efficacy, and would begin to provide explanations for the physical origins of particular quality disorders.